Project summary Human adults can improve their auditory perceptual skills through practice, making perceptual training a promising tool to treat communication disorders. However, the perceptual-training regimens currently used are costly in time, as well as in financial and human resources. This is due in large part to the commonly held view that only sensory experiences occurring during active training lead to learning. Challenging this view, preliminary studies for this proposal show that passive stimulus exposures that are otherwise ineffective, when temporally mixed with stimulus exposures occurring during active training, can enhance perceptual learning dramatically. This new finding reveals that learning can be facilitated by passive sensory experiences, and therefore that the cost of perceptual training could be significantly reduced. The long-term goal of this application is to determine the rules of learning on auditory perceptual skills. The current objective is to begin to delineate the circumstances under which experiences preceding and following a period of active training can contribute to efficient perceptual learning, and to identify the mechanisms for that contribution. The specific aims are to determine (1) to what extent, and (2) when and for how long, stimulus exposures can be presented passively during training and still benefit learning, (3) how the contribution of passively presented sensory experiences is related to an already known learning process, consolidation, and (4) the extent to which the proposed principles apply to visual and speech- perception tasks. These aims will be pursued by examining perceptual learning at a behavioral level in a series of novel training paradigms that are composed of both active task performance and passive stimulus exposure. Relevance The outcomes of the proposed studies, if as expected, could potentially lead to perceptual training regimens that yield maximal learning with minimal cost. Millions of people in the United States have a communication disorder, the majority of whom could benefit from perceptual training. Thus, the application of the proposed research could markedly improve public health.